1. Field of the Invention
This invention relates to improvements in syringes for effecting subcutaneous and intramuscular injections of medicaments and the like into human beings and animals and for taking blood samples therefrom.
2. Description of the Prior Art
Most syringes now used in hospitals, offices and health centers are of the disposable type, that is, they are disposed of or discarded after one use. These syringes usually comprise two pieces--a barrel and a plunger or piston mounted for reciprocable movement in the barrel. Both parts are usually made of plastic material. The barrel has a nozzle at the discharge end for the attachment of a hypodermic needle or cannula. On the plunger a sealing ring of rubber material is provided to act as a seal between the plunger and the inside surface of the barrel. Either the barrel or the plunger is provided with a scale by which the volume of liquid drawn into or dispensed from the barrel may be accurately determined.
As a disposable product a syringe of this type, although made by modern mass production methods such as injection molding, is relatively expensive due to the materials and precision involved in the manufacture thereof. Considering the enormous number of disposable syringes used over the world each year, estimated at several billions, the cost and waste of materials is significant and can hardly be justified. Any reduction in the manufacturing cost of a syringe, even if it amounts to only a fraction of a cent, can provide a large saving. Consequently, great efforts have been made and still are being made to lower the manufacturing costs of disposable syringes.
These efforts have not so far resulted in a radical change of the construction or the method of manufacturing of disposable syringes. They are still constructed as a two piece article which has to be thrown away in its entirety after having been used only once.
It has not been suggested so far to limit the disposable aspect to part of the syringe only; a readily apparent problem in connection therewith is the difficulty to maintain in a satisfactory manner the sterility of the syringe if a part thereof is to be used more than once.
It has been proposed to combine a barrel and a plunger with a replaceable container positioned at the discharge end of the barrel, the container being introverted or collapsed upon itself in use by action of the plunger to eject or administer the medicament contained in the container. Syringes of this type are disclosed in U.S. Pat. No. 978,488 to Roesch dated Dec. 13, 1910 and in U.S. Pat. No. 2,514,575 to Hein dated July 11, 1950. However, in these prior art syringes the container is a prefilled closed cartridge or capsule which is positioned in the barrel. The barrel is closed at the discharge end by a continuation of the barrel or by a separate end cap or like element. A discharge opening is provided at the discharge end to communicate with the attached needle or cannula.
A problem with this type of syringe is the possible contamination of the reusable elements following discharge of the cartridge or capsule contents. The expended cartridge or capsule must be withdrawn from the rear of the barrel or the end cap must be disconnected to permit cartridge or capsule removal. In either case, any contact of unexpended medicament with the reusable elements requires that these elements be cleaned and then sterilized. Additionally this type of syringe only permits discharge of the container contents and does not allow the medicament or the like to be drawn into the container under sterile conditions. This is a problem also for the injection apparatus disclosed in U.S. Pat. No. 3,308,818 to Rutkowski dated Mar. 14, 1967 wherein a container is located in a barrel which functions as a gas expansion chamber, and the container is introverted upon itself by gas pressure produced in said barrel by an explosive device.